FIG. 1 shows a mobile communication system consisting of a base station (BS) and n (n is a positive integer) user equipments (UE01, UE02 . . . , UEn).
In said mobile communication system applying CDMA technology with at least one base station and a group of UEs, if the uplinks of a plurality of UEs (referring to the radio links from UE to BS, that is, 1001, 1002 . . . 100n as shown in FIG. 1) are synchronized, the performance of the system would be greatly improved. 2001, 2002 . . . 200n shown in FIG. 1 represent the downlinks from the BS to each UE.
Now referring to FIG. 2, in the uplink synchronized CDMA system, synchronization of uplinks of each UE is typically established through the following steps:                (1) each UE sending a specific uplink synchronizing random access signal;        (2) BS detecting each uplink synchronizing random access signal, and obtaining the uplink timing information of each UE; then the BS transferring a timing synchronization adjusting command (synchronization adjusting information) to the UE through a specific downlink channel, such as FACH (Forward Access Channel);        (3) each UE adjusting its own timing based on said command and accessing the system in a specific access channel, such as RACH (Random Access Channel).        
Since a plurality of UEs are allowed to access the system at the same time, each UE usually adopts an orthogonal or quasi-orthogonal pseudo-random code (PN) as its uplink synchronizing random access signal. In a mobile communication system implementing the random access of multi-UE by adopting pseudo-random codes, based on the orthogonality of the pseudo-random codes, the BS can get the information of simultaneously accessed UEs through detecting the uplink synchronizing signals sent by each UE in the mobile circumstance.
In a mobile communication system consisting of at least one BS and a group of UEs, shown in FIG. 1, a set of (N) orthogonal or quasi-orthogonal pseudo-random sequence codes m1, m2 . . . mN (vectors) can be assigned to the BS, and one of said codes will be selected by one UE in the group. The set of orthogonal or quasi-orthogonal pseudo-random sequence codes satisfies the following correlation properties:
                    m        _            i        ·                  m        _            j        =      {                                                      L                                                      i                =                j                                                                                                          0                  ⁢                                                                          ⁢                  or                                ≈                0                                                                                      i                  ≠                  j                                ,                                                    ⁢                                  ⁢        i            ,              j        =                  1          ∼          N                    
wherein, the “●” represents dot product. The dot product of any two different orthogonal or quasi-orthogonal pseudo-random sequence codes (i≠j) in said set (N in number) is 0 or approximates to 0, and the dot product of any identical orthogonal or quasi-orthogonal pseudo-random sequence codes (i=j) in the set is a constant L.
The uplink synchronizing random access signal sent by UE contains a pseudo-random sequence code. On theoretic, with the correlation properties of the pseudo-random sequence codes, the BS can detect the uplink synchronizing signal of each UE by using various kinds of mature correlation operations, such as direct sequence convolution (linear correlation) or matched filtering, etc., combined at the same time with a series of relevant decision conditions.
Nevertheless, in the condition that the uplink synchronizing random access signal that UE adopts is orthogonal or quasi-orthogonal pseudo-random sequence code, there would be serious multi-path interferences in some mobile channels, and thus it is difficult to achieve complete orthogonality between different orthogonal and quasi-orthogonal codes, which make the signal detection more complex. Therefore, it is quite difficult to detect rapidly, reliably and accurately, the uplink synchronizing random access signals sent by a plurality of UEs.